What if instead of bringing the Goth date to the wedding Spike had saved the life of a classy upscale lady and brought her instead?  Say he saved the life of a Literature professor at Sunnydale University? How would bringing the upscale classy lady make Buffy jealous? 

The woman can be overjoyed when she finds out Spike was actually living during the timeframe of her favorite writer or poet. 

Buffy gets self conscious at how well the lady is put together and articulate she is.....plus the fact she did graduate from college.